Spreading, extruding, or like operations



Aug. 25, 1936..

F. RUCHAPPELL SBREADING, EXTRUDING, OR LIKE OPERATIONS Filed Oct. 10,1953 o ancewith the present invention, and I' Patented Aug. 25, 1936UNITED STATES- PATENT. OFFICE srnmnmc, nx'ranpmmon me ornns'rrons NewJersey Application October 10, 1933, Serial Na ssz su 6 Claims. (oi91-58 .This invention relates to. spreading, extruding or likeoperations, and more. particularly to such operations whereinamaterialis coated with an organic substance, such as rubber for example, from anaqueous dispersion-of the same. a

In generaL'materials may be coated with rube her or rubber-like materialfrom aqueous dispersions of the same, such as natural or artificiallatices, by electrolytic deposition processes or by 10 mechanicaloperations such as spreading, extrusion, dipping, spraying and thelike.In coatin fabric, for example; by electrolytic deposition,

. the material to be coated is passed between'positive and negativeelectrodes submerged in a bath of alkaline preserved latex containedwithin a receptacle, whereby the negatively charged rubber globules inanode and are deposited by electrophoresis upon.-

that side oftheinterposed fabric material which is remote from the:anode. Migration in the reverse direction of course takes place inthecase of an acid dispersion in which the rubber globules are positivelycharged and hence migrate.

toward the cathode. In coating sheet material,

on the other hand, for example by a mechanical operation, the-aqueousdispersion of rubber, preferably in the form of a thick paste, may befed to one face of the material, and spread evenly thereon by means ofan ordinary doctor knife or speeds, such spreading operations aresatisfactory, but when an attempt is made to speed up the passage of thesheet material beneath the spreader a rough uneven surface of the rubberdeposit results, since the dispersion pastetends to adhere to and uponthe spreader knife.

The present invention relates to such mechanical spreading orextrusionor like operations wherein a vconflning,and shaping'ordistributing member operates upon the aqueous dispersion to coata'substance with such dispersion or to shape the material. ;Ihe presentinvention is applicable to various types of apparatus but itwill bedescribed in detail, for convenience'as applied to rial, such as fabric,as shown in theaccompanying drawing, in which: I r

, Fig. 1 is a diagrarnm tic view partly in cross sectionof a device forcoating fabric 1l1-iiCc01'd- Figs. 2 and 3' are modifiedforms or ratus.shown in Fig. 1.

In carrying out the present invention, an electrical potentialdifference ismaintained between the dispersion and the confining, anddistributthe" latex migrate toward the likeapparatus and dried. Atrelatively slow.

the dispersion paste being extruded, or, in case the a spreadingapparatus for coating sheet mateinsulated of course from the body ofthemathe appaing or shaping member operating on the dispersion in thespreading, extruding, or like apparatus. It is foundthat when theconfining mem--. ber hasan electrical charge similar in sign to thecharge of the disperse phase of the dispersion, there is efiected anaccumulation of water at that edge or surface of the confining memberwhich is in contact withthe dispersion. This accumulation or film ofwater onthe con-- fining member acts as a lubricant and preventsadhesion of the dispersion to the confining memher and the formation ofincrustations, which would produce a rough-surfaced coating. In analkaline aqueous dispersion of rubber, the rubber particles arenegatively charged, and therefore 15 the confining member is made thecathode. The accumulation of water at the cathode is accounted for bythe fact. that the negatively charged particles in those portions of thecoating material which are adjacentto the cathodic shaping or spreadingmember tend to migrate away from the cathode and at the same time thewater tends to migrate toward the cathode, thereby producing adjacent tothe cathode surface athin layer or liquid-phase2which is relativelyfreeof the confining member and the dispersion enables the speed of travelof the material being coated, particularly in the. case of fabric, witha thick dispersion paste, to, be materially increased over the speedpracticable with previous spreading methods, and it also permits thesmooth spreading of such pastes as may be entirely too viscous to bespread smoothly by such previous spreading methods. 4

In a like manner a potential differencemay be maintained. between, onthe one hand, a metallic extrusion die, and on the other hand, thebodyof extrusion process is a coating operation, between the metallicdie and thematerial being coated,

such as a wire, for example. In. the case of the extrusion of adispersion paste to form .a thread, film. or sheet or like product, theextrusion die,

anode member. j

It is clear that the process of the present inventlon is wholly distinctfrom processes wherein 55 wire or the body of the machine-may serve asthe rubber from latex is cataphoretically precipitated upon a movingfabric, interposed between a cathode and a supporting member-containingwithin it an anode. The present process is fundamentally a mechanicalspreading process, wherein the migratory properties of dispersedparticles under the influence of an electric field, or potentialgradient, are utilized toprovide a thin layer of relatively dilutedispersion at-the contact surface between the dispersion and theconfinin and distributing or shaping member such as a spreader bar ordoctor, or extrusion die. The thickness of the coatings obtainable bythe present process is nowise dependent upon the conditions which wouldgovern the thickness of a coating deposited by electrophoresis upon asimilar backing. Such negligible electrophoretic deposition as may occurin the present process does not operate to increase the amount of rubberapplied to the backing but can only result in a slight coagulation,adjacent tothe backing, of the latex which has already been depositedthere by the mechanical action of the spreader bar.

Referring more particularly to the drawing, the invention is illustratedas applied to an apparatus for coating fabric wherein the fabricmaterial and the spreading means provide an extrusion orifice for thedispersion paste. This spreading apparatus illustrated in the drawingwherein the spreading means and the material to be coated form anextrusion orifice for the dispersion paste to be spread is the subjectmatter of the patent to Raymond J. O'Brien and Francis R. Chappell, No.1,972,457, granted Sept. 4, 1934, and no claim is made herein for suchapparatus perse.

In the apparatus of Fig. 1 a suitable sheet material' l,such as fabric,which it is desired to coat, is passed over an anvil roll 2, and under aspreader bar 3 which is positioned over the .anvil roll. The spreaderbar} is constructed of electro-conducting material and is insulated fromthe rest of the equipment and is connected to the negative pole of adirect current supply circuit by means'of lead 4. The positive pole ofthe supply circuit is connected by means of lead 5 to the anvil 2 overwhich the material to be coated is moved continuously by any'suitablemeans, not shown. The dispersion 6 which is to coat the material I, maybe an aqueous dispersion of rubber or rubber-like material, eithernatural or artificially prepared, or a dispersion of other dispersiblematerial in which the dispersed particles carry negative electriccharges. A wetting roll I isprovided for moistening the material to becoated, preferably with an electrolyte solution, so as to insure itsbeing electroconductive. When the material is electroconductive-per sethe wetting roll may be eliminated, if desired.

In the modification shown in Fig. 2, a spreader bar or knife 3 isconnected to a suitable source of current by the lead 8 and is made thecathode as in Fig. 1. The positive pole of the current supply isconnected to a fixed electrode 9 arranged to contact with, the mass 6 ofthe dispersion to'be spread, either in the position shown, or in asupply tank which may be provided adjacent the spreader knife 3. In thismodification a potential difference is thus maintained directly betweenthe spreader knife 3 and'the bodyof the dispersion, so that the anvilroll 2 and the material being coated are not utilized to complete thecircuit;

hence such apparatus as is shown in Fig. 2 may also be used for coatingsheets of non-conductive material such as rubber and the like, as wellas fabric,- paper, etc.

In the modification shown inFig. 3 the spreader knife 3 is again thecathode while the anode is in the form of a contact roll it makingelectrical contact'with a surface of the material to be coated, afterthe latter has been moistened by means of a wetting roll 1 or renderedelectroconductive, if necessary, in any other suitable manner.

In the various figures the spreader knife has been made the cathode,whereby the dilution of a dispersion of negatively charged particleswill be effected at the contacting surface of the spreader knife, thusproviding lubrication between the dispersion and the spreader knife.

It is obvious that in spreading or extruding a dispersion paste whereinthe dispersed particles are positively charged, such as a so-called acidlatex and other rubber and like dispersions havmg a pH of less than14.5, lubrication of the condesired to obtain. It has been found thatpotential differences of up to 220 volts are satisfactory for mostpurposes. Such voltages lower than 220 volts may be used as areconsistent with the speed at which it is desired to operate thespreading machine and of course depending on the concentration,viscosity and conductivity of the paste to be spread.

While specific embodiments of the invention have been described, it isobvious that numerous modifications may be made therein and it is notdesired to limit the invention otherwise than as set forth in theappended claims. I Having thus described: my invention, what I claim anddesire to protect by Letters Patent is: 1. In a spreading, extruding orlike operation, the method of preventing adhesion between an 1 aqueousdispersion of an organic substance and distributing or shaping memberand said disper-- sion, theelectrical charge cnthe eonfining, and

' shaping or distributing member being similar in sign to the charge onthe particles of the disperse phase of the dispersion, whereby alubricating film of-the dispersion of greater fluidity than the body ofthe dispersion is maintained at the interface of the dispersion and theconfining, and distributing or shaping member by electrophoresis.

2. In the process of coating material with an aqueous dispersion of anorganic substance by means of a confining and distributing member fromwhich such dispersion emerges from frictional contact therewith, thestep of maintaining an electrical potential difierencebetween saidconfining and distributing member and said dispersion, the electricalcharge on 'the confining and distributing member being similar in signto the charge on the particles of the disperse phase of the dispersion,whereby a lubricating film of the dispersion of greater fluidity thanthe body of the dispersion is maintained at the interface of thedispersion and the confining, and distributing member byelectrophoresis.

3. The method of coating material with an organic substance whichcomprises spreading an aqueous dispersion of such organic substance onthe material by means of a confining and distributing member from whichthe dispersion emerges from frictional contact therewith, andmaintaining an electrical potential diilerence between the confining anddistributing member and the dispersion, the electrical charge on theconfining and distributing member being similar in sign to the charge onthe particles of the disperse phase of the dispersion, whereby alubricating film of the dispersion of greater fluidity than the body ofthe dispersion is maintained at the interface of the dispersion and theconfining and distributing memberv by electrophoresis.

4. The method of coating material with an organic substance whichcomprises 7 pressing an aqueous dispersion of such organic substance onthe material by means of a distributing member from which'the dispersionemerges from frictional contact therewith, and maintaining an electricalpotential difference between the pressing means the interface of thedispersion and the pressing and distributing member by electrophoresis.

5. The method of continuously coating sheet material with an aqueousdispersion of an organic substance which comprises moving the sheet ma-,which the dispersion emerges from frictional contact therewith andspreading such dispersion on the sheet material while maintaining anelectrical potential diflerence between the distributing member and thedispersion the electrical charge on the distributing member beingsimilar in sign to the charge on the particles of the disperse phase ofthe dispersion, whereby a lubricating film of the dispersion of greaterfluidity than the body of the dispersion is maintained at the interfaceof the dispersion and the distributing member by electrophoresis.

6. In an apparatus for spreading or extruding an aqueous dispersionpaste, an electro-conductive confining, and distributing or shapingmember for the dispersion and from which the dispersion emerges infrictional contact therewith, means for supplying to the. confining, anddistributing or shaping member an electrical charge which is similar insign to the charge on the particles of the disperse phase of thedispersion, and means for supplying an electrical charge of a diiferentpolarity to the dispersion to maintain an electrical potentialdifference between the confining,-and distributing or shaping member andthe body of the dispersion in contact therewith, whereby a lubricatingfilm of the dispersion of greater fluidity than the body of thedispersion is maintained at the interface of the dispersion and theconfining, and distributing or shaping memher by electrophoresis. I

FRANCIS R. CHAPPELL.

